(1) Field of the Invention
The present invention relates to a system and method applicable to an autonomous vehicle for autonomously controlling steering response according to vehicle speed.
(2) Background Art
U.S. patent applications Ser. No. 337,707 and No. 485,910 filed on Apr. 13, 1989 and Feb. 27, 1990 respectively, exemplify structures of autonomous vehicles.
In previously proposed vehicle speed sensitive steering response control systems, a driving control response model for a vehicle, based on a mathematical model `driver` virtually emulating a human driver, includes: a "linear feedback correction steering model" which detects relative distance between a lateral position of the autonomous vehicle and a detected width of its running path and a posture angle based on the posture of the vehicle relative to its running path and adjusts the steering response according to the detected information; a "predictive control model" which predicts the future position of the vehicle `L` meters ahead, according to the current posture angle; "optimium control model" which maximizes or minimizes a set evaluation function, i.e., changes the control response according to a vehicle characteristic when the evaluation function is set. The validities of all control models are established through experimentation.
Since in previously proposed vehicle-speed dependent steering response control apparatuses proportional constants for adjusting the steering angle are arbitrarily set, disadvantages in terms of both vehicle stability and follow-up characteristics are created, as no sufficient adjustment thereof is carried out while the vehicle is in motion. In cases where these models have been applied to autonomously running vehicles with the vehicle speed being variable, means for determining optimum proportional constants both in terms of stability and follow-up characteristics has not been defined. Therefore, these models are effective only in a case where the vehicle cruises at a substantially constant speed.